The invention pertains to a rotor disk according to the generic part of Claim 1.
Several configurations of such rotor disks are known in prior art. They are mostly arranged near the floor of a receiving container or cutter compactor to treat and process thermoplastic polymers and consist substantially of a disk-shaped tool carrier on whose top surface mixing and/or comminuting tools are provided. During operation, the disk turns and the tools grasp and if appropriate comminute the plastic material presented in the container while heating it at the same time. Furthermore, the material is mixed and continuously agitated such that a mixing spout is formed in the container.
In principle, means to process polymers are also known in prior art, for example from AT 375 867 B, AT 407 970 B or WO 93/18902. With the revolving tool carriers or tools, the treated plastic material is hurled against the side wall of the container. Some of this plastic material climbs up along the side wall of the container and revolves in the form of a mixing spout, but eventually it drops back into the center of the container. This results in the desired dwell time of the treated plastic particles in the receiving container, such that the plastic material discharged into it is well mixed, adequately heated through the frictional forces that occur, and—in the case of tools which comminute the plastic material—also adequately comminuted.
However, it has been found that not all the plastic material hurled against the container side wall adheres, but that a portion drops down below the lowest tool, i.e. under the disk that forms the lowest tool carrier. There, that portion of the plastic material can attach itself through friction.
It has been tried to avoid this disadvantage by providing conveying ribs on the lower face of this disk. In that respect, it is known in prior art to provide straight and radial ribs on the lower face of the disk or the tool carrier whose purpose it is to convey plastic material that drops into the section between the floor of the cutter compactor and the lower face of the tool carrier to the outside again and to remove it from that sector.
However, that measure has not been fully satisfactory. In particular with receiving containers of large dimensions and a correspondingly large filling volume of several hundred kilograms of polymer material, sufficiently large disks of large diameters must be used. On the one hand, these disks must have very close tolerances, and they must rotate very quietly and evenly, since the distance between the disk and the floor measures only a few millimeters. In such large-format cutter compactors, there are very high requirements for the conveying performance of the ribs because—as mentioned—there is a large volume of material to be processed which on the one hand must be moved and which on the other hand, due to its own weight, is pushed hard downward and into the section between the disk and the floor.
In upgrading such arrangements it has been shown that the conveying performance of known disks, which still function adequately in smaller containers, is no longer sufficiently able in large containers to keep the material from the critical section. Furthermore, the rpm of the mixing tools that is necessary to provide the material with an upward impetus and to increase dwell time cannot be randomly increased, since the higher friction would again cause greater heat, which could lead to a local melting of the flakes.
Again and again, polymer flakes enter the outer section between the floor and the disk where they remain permanently. This raised the temperature in that section, the flakes agglomerate, become sticky and may even melt, which causes more flakes to stick together. After some time, the disk begins to rattle, and finally it will come to a stop. It is therefore desirable that—should a particle become caught between the ribs and the container floor—this particle should become free again as soon as possible and that it is subsequently removed effectively from the critical sector.
Furthermore, it is not only fairly large flakes, but also quite small dust particles that enter the critical sector below the disk, whereby the dust particles advance much farther in the direction of the disk, where they remain. These fine polymer particles, too, will become too hot, and they will be isolated and captured in the critical sector.
In principle, this is also problematic with disks of smaller diameter, since smaller rpm, i.e. a relatively slow peripheral speed, is used, especially when heavier material is processed.